It was put together by Jason Perry, who actually works with the Cassini mission but in his spare time stitched together 66 images from the MDIS narrow angle camera from the MESSENGER mission’s second flyby of Mercury in October 2008, along with some data from the Mariner 10 mission in the 1970’s. The full file is 20 MB, with a resolution of 0.6 kilometers (0.37 miles) per pixel. What fun! —for us, that is. It took Perry four days just to set up his software, according to Emily Lakdawalla at the Planetary Society Blog.